Kubota LA 302 loader boom won't drop

   / Kubota LA 302 loader boom won't drop #1  

ArtySee

New member
Joined
Mar 25, 2023
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1
Tractor
Kubota B7500
I bought a used Kubota B7500 (about 2800 hours) with HST transmission and with an apparently factory- or dealer-installed LA 302 FEL, and a Woods backhoe attachment with hydraulic pump driven by the rear PTO. I have put about 500 hours on it since I bought it and the loader was working fairly well except there was no boom float (the joystick stopped before moving to the boom float position and I didn't even know the FEL had boom float) when the boom abruptly refused to go down - and I think the engine sounded like it was loaded-down. When I shut down the engine, I could get the boom down by moving the joystick to the boom-down position and the boom slowly settled.

I cleaned and resealed the control valve, and installed a detent kit for the rust-jammed parts (seems like the boom detent, and the positioning spring construction on both spools, are designed to get water in them and rust-up). All of the control valve seals showed some wear, but I didn't find a smoking gun for the boom problem. And because the boom cylinders were weeping, I resealed them too. I did not change any hoses or quick disconnects. I reinstalled everything and the bucket fill and dump operates OK, but the boom still will only go up and still refuses to go down with the engine running (except now boom float works, so that lets the bucket down in slow free-fall). The engine still sounds like it is loaded-down.

I have a parts manual but I don't have the FEL hydraulic circuit diagram.

I am open to any guidance.

Thanks,

ArtySee

Later 3/25/23:

Hey Y'all,

I flipped through the tractor manual and saw the discussion about the tractor hydraulics. It was in the back of my mind at dinner when a light went on. I got up from the dinner table and went out to check the tractor and found that the 3-point hitch hydraulic lever to the right of the seat had been bumped into the down position (had to be me that did it). As far as I know the 3-point hitch is frozen from disuse and won't move because the backhoe attachment has been in place for the life of the tractor. I moved the lever to neutral, started the engine, and voila! the loader boom goes up AND down, and the engine doesn't sound loaded-down.

I probably won't soon forget that lesson. And when the tractor dies, I'll salvage a really nice, rebuilt control valve. In the mean time, think I will put a strap on the 3-point hitch lever so it can't be bumped into working position.

ArtySee
 
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   / Kubota LA 302 loader boom won't drop #2  
Normally it's moving the three point control to the fully up position that puts the hydraulics into bypass mode. I believe the fix is normally to adjust the rock shaft.
 
   / Kubota LA 302 loader boom won't drop #3  
Suspect any quick connects in hoses going to loader cylinders. First open and re-set the connectors.

If problem persists, swap loader arm hoses for bucket hoses to see if problem now moves to the bucket operation.

Quick connects can and do fail internally.

When swapping hoses, take great care in marking where the hose was in the beginning and then for each change. It is very easy to get them mixed up and now you have a bigger problem

Dave M7040
 
   / Kubota LA 302 loader boom won't drop #4  
Marine grade shrink tube does a good job of marking hydraulic lines. It appears to be stable when exposed to hydraulic fluid, and you can get it in multiple colors.
 
 
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